1. Field of the Invention
The present invention generally relates to a light beam scanning device used in a copier, a printer, a facsimile apparatus or the like in an electrophotographic system or an electrostatic recording system.
2. Description of the Related Art
As related arts in this field, for example, Japanese Laid-Open Patent Application No. 3-274015 discloses a method in which synchronization detection signal of two beams is decomposed and distributed, and, states of the two beams are determined by using timer means, and, Japanese Patent No. 2880120 discloses a method of gating a synchronization detection signal by a synchronization detection modulating signal.
However, the related art disclosed by Japanese Laid-Open Patent Application No. 3-274015 relates to a method to be applied to an image forming apparatus of a single color in which scanning on two lines is performed simultaneously. Accordingly, this method cannot be applied to a color image forming apparatus in which scanning is performed for a plurality of colors of lines in an order of the respective colors (color components).
The present invention is devised in order to solve the above-mentioned problem, and, an object of the present invention is to provide a light beam scanning device by which, even when beams of more than one color (color component) are applied to a common synchronization detecting sensor, output pulse series of the synchronization detecting sensor can be positively classified/separated into synchronization detection pulses of the respective color components.
A light beam scanning device according to the present invention for scanning a recording medium (photosensitive body) by a light beam so as to perform recording of information thereon, includes:
a synchronization detecting sensor to which light beams of a plurality of colors are applied with difference in time;
a signal generating circuit which generates a signal which is active only during an interval of taking one pulse of a series of output pulses of the synchronization detecting sensor, but is not active during an interval of taking more than one pulse thereof; and
a signal separating circuit which separates a synchronization detection pulse for each color only when the signal generated by the signal generating circuit is active.
Thereby, it is possible to employ a synchronization detecting sensor which is common for a plurality of colors (color components). Accordingly, the costs can be effectively reduced.
The signal generated by the signal generating circuit may be a synchronization detection beam-turning-on signal for each color.
The separating circuit may be provided for each color, and has a same circuit configuration, and, each separating circuit has information externally set for indicating an order of the colors (color components) in the series of pulses output from the synchronization detecting sensor so as to take a pulse thereof corresponding to a respective one of the colors. Thereby, as the common circuit configuration can be used for the respective separating circuits, the costs can be effectively reduced.
The synchronization detection beam-turning-on signal for the advancing first color may become active when a first main-scanning counter counts a first predetermined number, and, may become inactive when an initial value is loaded into the first main-scanning counter by the synchronization detection pulse corresponding to the first color; and
by the synchronization detection pulse corresponding to the first color, a second main-scanning counter for the subsequent second color may be loaded with an initial value, and the synchronization detection beam-turning-on signal for the second color may become active when the second main-scanning counter counts a second predetermined number, and, may become inactive when the initial value is loaded into the second main-scanning counter by the synchronization detection pulse corresponding to the second color.
In this configuration, as only initialization of the main-scanning counter of the subsequent color is made by the pulse of the advancing color, the costs can be effectively reduced.
A beam of which color has an error may be detected by using the synchronization detection pulse corresponding to each color.
Thereby, it is possible to prevent an abnormal image from being formed due to erroneous or lack of proper beam generation.
When the synchronization detection pulse corresponding to the advancing first color has an error, the synchronization detection pulse corresponding to the subsequent second color may be prevented from being output. Specifically, when the first pulse of the pulse series is not output, all the other pulses thereof are not output from the separating circuit(s).
Thereby, even when error occurs in synchronization detection signal successively for different colors (color components), detection of the error can be performed properly.
While the synchronization detection pulse corresponding to the subsequent second color is not output, the second synchronization detection beam-turning-on signal may be made inactive when the second main-scanning counter counts a predetermined error-detection number.
Thereby, it is possible to prevent an abnormal image from being formed due to erroneous or lack of proper beam generation.
Each separating circuit may output synchronization detection pulses selectively of one of single-beam system and a multi-beam system according to a set number of beams.
Thereby, it is possible to utilize the device for both a single-beam system and a multi-beam system, and to effectively reduce the costs.